Alternator Controller

ABSTRACT

In one embodiment, a generator includes a rotor configured to rotate in cooperation with a stator to generate electrical power. A sensor, which is supported by the rotor, is configured to generate a trigger signal indicative of a position of the rotor. A communication interface is configured to receive the trigger signal from the sensor of the rotor and receive data indicative of an output of the generator. A controller supported by the rotor or configured to perform a phase analysis of the trigger signal and the output of the generator and calculate a power angle for the generator based on the phase analysis.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/084,890, filed Nov. 26, 2014, which is hereby incorporated byreference in its entirety.

FIELD

This application relates to the field of alternators, and morespecifically, a rotor mounted controller for an alternator.

BACKGROUND

An engine-generator set, which may be referred to as a generator or agenset, may include a prime mover (e.g., an internal combustion engine)and an alternator or another device for generating electrical energy orpower. One or more generators may provide electrical power to a loadthrough a power bus. The power bus, which may be referred to as agenerator bus or common bus, transfers the electrical power from theengine-generator set to a load.

A current transformer may measure the alternator current on thegenerator bus. A current transformer includes a primary winding, amagnetic core, and a secondary winding. The primary winding may be theconductive path of the generator bus. The secondary winding may be alength of wire wrapped around the magnetic core. The magnetic core maybe placed around the power bus or clamped to the power bus. Current inthe power bus induces a proportional current in the secondary winding,which may be measured using an ammeter or other instrument.

However, current transformers have many drawbacks. Current transformersare expensive. Current transformers are bulky and require significantspace. The installation of current transformers is labor intensive andprone to error. An alternative the current transformers for generatorsets is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are described herein with reference to thefollowing drawings.

FIG. 1 illustrates an example rotor assembly.

FIG. 2 illustrates an example stator assembly.

FIG. 3A illustrates an example load characterization circuit.

FIG. 3B illustrates another example load characterization circuit.

FIG. 4A illustrates an example flowchart for load characterization.

FIG. 4B illustrates an example circuit for load characterization.

FIG. 5A represents a chart for an example transient response.

FIG. 5B illustrates another example chart for an example transientresponse.

FIG. 6 illustrates an example rotor controller.

FIG. 7 illustrates an example chart for a transient response of therotor controller at partial load.

FIG. 8 illustrates an example chart for a transient response of therotor controller at full load.

FIG. 9A illustrates an example three-phase rotor.

FIG. 9B illustrates an example single phase rotor.

FIG. 10 illustrates an example plot for the single phase rotor of theFIG. 9B.

FIG. 11 illustrates another example rotor controller.

FIG. 12 illustrates an example circuit board of FIG. 11.

FIG. 13 illustrates another example rotor controller.

FIG. 14 illustrates another example rotor controller.

FIG. 15 illustrates an example arrangement of magnets for rotorposition.

FIG. 16 illustrates an example plot of a trigger for the example of FIG.15.

FIG. 17 illustrates another example rotor assembly.

FIG. 18 illustrates another example rotor assembly.

FIG. 19 illustrates an example flow chart determining a generatorparameter based on the trigger.

FIG. 20 illustrates another example arrangement of magnets.

FIG. 21A illustrates an example non-linear load.

FIG. 21B illustrates an example flowchart for calculating a frequencybased on the non-linear load.

FIG. 22 illustrates another example rotor controller.

FIG. 23 illustrates an example flowchart for calculating armaturecurrent by a rotor controller.

FIGS. 24A-B illustrate vector geometry for stator current calculation.

FIG. 25A illustrates an example chart for a field speed profile based onthe trigger.

FIG. 25B illustrates an example field current correction.

FIG. 26 illustrates an example total harmonic distortion correction.

FIG. 27 illustrates an example rotor side component of a communicationsystem.

FIG. 28 illustrates an example stator side component of a communicationsystem.

FIG. 29 illustrates an example set of selectively activate damper bars.

FIG. 30 illustrates an example onboard rotor controller.

DETAILED DESCRIPTION

FIG. 1 illustrates an example rotor assembly 600. The rotor assembly 600may include an exciter armature 601, a field coil assembly 602, acooling fan 603, drive discs 604, a coupling 605, a rotor controller606, a sensor 607, a rotor communication device 608, and a rotor bearing609. Additional, different, or fewer components may be included.

The coupling 605 and/or drive discs 604 couple the rotor assembly 600 toa prime mover such as an engine. The coupling 605 is a fixed connectionbetween the rotor assembly 600 and the engine via drive discs 604. Theengine turns the rotor assembly 600, rotating the exciter armature 601along with the field coil assembly 602. The engine may also turn thecooling fan 603. The cooling fan 603 forces air across the field coilassembly 602, the rotor controller 606, and/or the exciter armature 601,any of which may expel heat as current flows through the windings orother electrical components.

FIG. 2 illustrates an example stator assembly 610. The stator assembly610 includes a stator chassis 611, a set of leads 612, armature windings613, an end bracket 614, an exciter field assembly 615, and a statorcommunication device 618. Additional, different, or fewer components maybe included. The rotor assembly 600 fits inside the stator assembly 610.The exciter field assembly 615 is aligned with the exciter armature 601.The stator chassis 611 is aligned with the field coil assembly 602.

The exciter armature 601 includes exciter armature windings, and theexciter field assembly 615 includes a source of magnetic flux, such aseither permanent magnets or windings. As the exciter armature windingsrotate within the stator assembly 610, one or more currents aregenerated in the exciter armature windings. Two or more wires or otherelectrically conductive connections connect the exciter armaturewindings to the field coil assembly 602. The current from the exciterarmature windings supplies current to the field coil assembly 602. Asthe field coil assembly 602 rotates within the stator assembly 610,currents are generator in the armature windings 613. The current fromthe armature windings 613 is carried by the leads 612 to a load.

Communication between the stator and rotor is provided by the rotorcommunication device 608 and the stator communication device 618. Thecommunication may take various forms including but not limited tooptical communication, radio communication, and magnetic communication.The communication may be any form in which the communication path isair. Thus, no wires connect the rotor communication device 608 and thestator communication device 618. When the communication is opticalcommunication, the rotor communication device 608 includes a lightsource (e.g., light emitting diode) and a photoreceptor, and the statorcommunication device 618 includes a light source and a photoreceptor.Light emitting on one side of the communication path is detected on theother side of the communication path. When the communication is radiocommunication the rotor communication device 608 includes a transceiverand the stator communication device 618 includes a transceiver. Radiosignals generated at the stator communication device 618 are received atthe rotor communication device 608, and vice versa. When thecommunication is magnetic communication, the rotor communication device608 includes an arrangement of magnetic coils. An alternating currentflowing through the magnetic coils is controlled to transfer data to thestator communication device 618 by inducing a magnetic flux in coils inthe stator communication device 618. The amplitude of the alternatingcurrent in the stator communication device 618 is measured or sampled todetect the transferred data. Communication may similarly be performed inthe direction from the stator communication device 618 to the rotorcommunication device 608.

The communication interface can pass a digital signal (such as a targetfield voltage, target field current, stator voltage, stator current,alternator type, environmental conditions, or other similar statorparameters) where the signal level contains two states and isinterpreted, sampled, decoupled, or multiplexed or an analog signal(such as stator voltage or stator current) where the signal amplitude orfrequency is measured by taking and processing samples to measure aquantity.

The rotor controller 606 may receive sensor data from one or moresensors and in response, generate one or more generator commands. Thesensor data may be a measurement of an electrical parameter of theexciter armature 601, or the field coil assembly 602. The electricalparameter may include a current, a voltage, or a resistance. Theelectrical parameter may be a flux induced on the field coil assembly602 by a current in the armature windings 613. In this way, the sensordata may be indicative of an output of the generator. Further, because aload on the generator impacts the current in the armature windings 613,the sensor data may be indicative of the load on the generator. Thesensor data may be temperature data, which may indicate the resistanceof the field coils or armature windings. The sensor data may be magneticdata measured on damper windings of the rotor, parallel or perpendicularto the primary rotor flux. The sensor data may describe a physicalposition of the rotor in any direction or a capacitance that is relatedto proximity to a surface, the sensor data may be acceleration data orstrain data measured on the rotor, or the sensor data may be adeflection measurement on any axis or mode.

The rotor controller 606 may perform an analysis of one or morecomponents of the sensor data at the controller. For example, the rotorcontroller 606 may compare a value in the sensor data to a threshold.The rotor controller 606 may sort, average, or filter the sensor data.The rotor controller 606 may remove outlier values from the sensor data.The rotor controller 606 may calculate a moving average of the sensordata. The rotor controller 606 may query a lookup table using the sensordata.

The rotor controller 606 generates a generator command at the controllerbased on the sensor data. The generator command may be an adjustment ina current in the field winding of the rotor, which directly affects theoutput of the generator. For example, the rotor controller 606 maycompare an estimated output voltage or current of the generator to athreshold. When the output falls below a low threshold, the rotorcontroller 606 increases the current of the field windings. When theoutput exceeds a high threshold, the rotor controller 606 decreases thecurrent of the field windings. The generator command may adjust a speedof a prime mover (e.g., engine) driving the rotor of the generator. Forexample, the rotor controller 606 may compare an estimated outputfrequency of the generator to a threshold. When the output frequencyfalls below a low threshold, the rotor controller 606 increases thespeed of the prime mover. When the output frequency exceeds a highthreshold, the rotor controller 606 decreases the speed of the primemover. The rotor controller 606 may also identify an anomaly from thesensor data and generate a command to shut down the generator or issue awarning to the user.

The generator may also include one or more of a fuel supply, a coolingsystem, an exhaust system, a lubrication system, and a starter.Additional, different, or fewer components may be included. Thealternator may be an electromechanical device including a rotatingmagnetic field and a stationary armature, a rotating armature with astationary magnetic field, or a linear alternator. The prime mover maybe powered by liquid fuel (e.g., gasoline, diesel fuel, or others) orgaseous fuel. The gaseous fuel may be liquefied petroleum gas (LPG),hydrogen gas, natural gas, biogas, or another gas. The LPG may be orinclude primarily butane, primarily propane, or a mixture of hydrocarbongases. The hydrogen gas may include hydrogen mixed with air or oxygen.The hydrogen gas may be mixed with another fuel when delivered to theprime mover. Natural gas (e.g., compressed natural gas (CNG)) may be ahydrocarbon gas mixture. Biogas may be a gas produced by the breakdownof organic material. Other variations are possible.

The current or voltage of the rotating field winding on a synchronousalternator can be monitored to detect changes in load connected to thewindings of the stationary armature.

Various structures are available for the mechanical construction of thesynchronous alternator, including those illustrated in FIGS. 1 and 2. Inone representation, a synchronous alternator consists of a rotor and astator. The rotor has a field winding, which may be a series wound coilon a magnetically permeable core. The rotor may freely rotate within astator, about a concentric axis. The stator consists of armaturewindings; these are distributed coils placed on the interior of a stackof ringed laminations. The laminations include slots for the placementof the armature windings. The clearance between the freely rotatingrotor and the stationary stator is denoted as the air gap.

The function of the synchronous alternator is to convert mechanicalpower from a driving mechanism into electrical power. The drivingmechanism is denoted as the prime mover (e.g. internal combustionengine) and provides torque to the rotor. Electrical power is drawn fromconnection to the ends of the armature windings. This connection may becrimped terminals, wire splicing, or another fastening mechanism.

In order to convert mechanical power to electrical power, there ismagnetic coupling between the rotor and stator. This coupling is denotedas flux linkage; mathematically, flux linkage is the product of currentand inductance. The magnitude of the flux linkage in each winding has aself-component corresponding to a self-inductance and a mutual componentcorresponding to a mutual inductance. The mutual flux linkage componentprovides coupling between the rotor and stator. To generate voltage, themagnitude of flux linkage must be changing within a winding. Thismagnitude of the change can be the consequence of a change in windingcurrent or in physical displacement of a vector flux density (vectorquantity denotes magnitude and direction, which may be a rotation of therotor relative to the stator). Steady state operation of the synchronousalternator with a balanced three phase load maintains a constant fieldwinding current (DC value) and displaces the field winding relative tothe armature windings as the rotor rotates. The flux density generatedby the field winding is ortho-normal to the open area of the winding;thus, it is a vector quantity.

It is conceptually helpful to consider superposition when discussing thebehavior of a synchronous alternator. When there is no load connected tothe armature windings, this is denoted as an open-circuit scenario. Inan open-circuit scenario, the only contributor to the mutual fluxlinkage is the current flowing through the field winding (there is nocurrent flowing through the armature windings). The product of thiscurrent with the mutual inductance and rotational speed generatesvoltage in the armature winding.

When there is a load connected to the armature windings, there iscurrent flowing through the armature windings. This creates anadditional mutual flux linkage component that is in opposition to theflux component from the field winding; this flux linkage is denoted asarmature reaction. By superposition, the sum of the flux linkagecomponent and the flux component from the field winding equals the totalmutual flux linkage. To maintain a constant voltage on the armaturewinding, the magnitude of the mutual flux linkage component sourced fromthe field winding is increased to overcome the armature reaction.Adjusting field winding current to maintain a nominal armature windingvoltage is the primary function of the voltage regulator, which is anexample of a stator controller or stationary controller. The statorcontroller, or the functions described for the stator controller, mayalso be performed by the rotor controller if the output voltage of thegenerator is supplied to the rotating board.

As a conceptual exercise, a synchronous alternator with current flowingonly in the armature windings can be considered. In this case, the fieldwinding is not connected to a source; voltage is monitored at its ends.As the rotor is rotated within the stator, the flux linkage due toarmature currents will generate voltage in the field winding. If thisfield winding is connected to a load (such as the source impedance of anon-ideal voltage supply), then current will flow in the field winding.

Considering the three above steady-state scenarios, it should be evidentthat the voltage on and current flowing through the field winding isrelated to both the field winding supply and the current flowing throughthe armature.

The transient dynamics of the synchronous alternator describe thebehavior of the alternator as the load on the armature windings changes.It is helpful to consider the dynamics as the synchronous alternatormoves from a steady-state open-circuit scenario to a loaded scenario. Tobegin, it is necessary to introduce the law of constant flux linkages:this dictates that the flux linkage immediately before and immediatelyafter a transient event is constant (it is noted that this is the driverfor the principle, current flowing through an inductor cannot changeinstantaneously—this is for a single current path). When load isintroduced at the armature winding terminals of the synchronousalternator, current will begin to flow into the load; this creates anarmature reaction component. For the law of constant flux linkage tohold, the product of the sum of currents in the field and armaturewindings with the mutual inductance must remain constant. None of theconstituent components are inherently sufficiently stiff to be constantwith a changing armature current: field winding current and the mutualinductance will both change. Mutual inductance is the product of thenumber of turns on a winding divided by the magnetic reluctance in themagnetic circuit path. The reason for the mutual inductance change istwofold:

First, there is a damper winding that will be introduced into the mutualinductance equation to counteract asynchronous flux linkage components.This acts as an additional set of turns. Second, the magnetic reluctancepath will change as the load angle of the alternator changes.

The field winding will operate concurrently with the damper winding tocounteract the armature reaction; it cannot be excluded from themagnetic circuit. The magnitude of the field winding current willincrease (even in the absence of any action from the voltage regulator)as a result of the necessity to maintain a constant mutual flux linkage.

As mentioned previously, the primary function of the voltage regulatoris to maintain a nominal voltage on the terminals of the armaturewinding. When load is introduced and current begins to flow, thisarmature winding voltage decreases. The voltage drop may be detectedafter one or more periods of the AC waveform have occurred after theload change. The change in field winding current and/or mutualinductance may be monitored and analyzed to detect load change. In oneembodiment, the voltage regulator reacts more quickly and effectsreduced voltage dip and/or reduced time to return to nominal voltage.

FIGS. 3A and 3B illustrate an example block diagram for a system fordetecting changes in field winding current caused by increased armaturewinding current in the stator or the mutual inductance caused by thesame current increase in the armature winding. As a result of theincreased armature winding current, the field current (and/or associatedmutual inductance) changes; as a result of the increased armaturewinding current, voltage decreases.

The system includes a field winding 10, and an armature winding 12,which are separated by air gap 11. In one embodiment, as shown by FIG.3A, the sensor 14 may be connected to the field winding 10, formeasuring an electrical characteristic of the field winding 10. Thevoltage regulator 16 receives the measurement from the sensor 14, andcalculates a control signal based on the measurement. In one embodiment,as shown by FIG. 3B, the armature winding 12 is connected to a sensor 14for measuring an electrical characteristic of the armature winding 12.Example electrical characteristics include, voltage, current, andinductance.

FIG. 4A illustrates an example flow chart for the systems of FIGS. 3A or3B. At act S101, the current of the winding, either field winding 10 orarmature winding 12, is detected, either directly or through anotherproperty.

At act S103, a controller (e.g., voltage regulator or activator)calculates a load value from the change in winding current. The changein load depends on the mutual inductance between the field windings andthe stator windings. The inductance of the field windings may beprovided from the resistance and an alternator time constant. Thealternator time constant may be the resistance divided by theinductance, which may be computed based on the time required to reach apredetermined amount (e.g., 63%) of a final value with a step input.Alternatively, the inductance of the field windings may be based on aphase angle between an imposed voltage and current. The inductance ofthe stator windings may be similarly calculated using either of thesetechniques.

The mutual inductance between the field windings and the stator windingsmay be calculated based on the characteristics of the rotor and stator.Factors in determining the mutual inductance include the phaserelationship between the rotor and the stator, the rate of change of thevoltage in the rotor or stator, the rate of change of the current in therotor or stator, a change in the measured rotor inductance, and/or achange in the measured stator inductance. The mutual inductance (M) maybe calculated based on a coupling factor (K), the stator inductance(L_(stator)) and the rotor inductance (L_(rotor)) according to Equation1:

M=k*√{square root over (L _(stator) *L _(rotor))}  (1)

Thus, the mutual inductance is the parallel factor for the contributionof the stator inductance to the rotor inductance or the statorinductance to the rotor. The mutual inductance may be measuredempirically by applying a range of voltage and currents to the statorwindings and measuring the response on the field windings from currentchanges in the stator windings. In one example, the mutual inductancefrom a current on the stator winding (stator-rotor inductance) thatinduces a voltage in the field winding is different than the mutualinductance from a current on the field winding (rotor-stator inductance)that induces a voltage in the stator windings.

The load on the stator may be determined from the changes in current.For example, a lookup table for the generator indexed by model number,manufacturer, or physical characteristics may associate stator windingcurrents, or changes in stator winding current to generator load orchanges in generator load. Thus, the lookup table may include athreshold value for the electrical characteristic of the alternator formultiple alternator models, manufacturers, or types. The regulator (orstator controller) may access the lookup table using the model,manufacturer or type and receive a threshold value for the change inelectrical characteristic.

Alternatively, the load may be calculated based on a mathematicalrelationship between current and load. However, the load calculation maybe omitted (as described below, field current may be calculated directlyfrom stator current).

At act S105, the controller calculates a field current adjustment basedon the load value from act S103. The field current adjustment may bebased on a coupling ratio, or mutual inductance, related to the numberof turns on the stator windings and the number of turns on the fieldcurrent windings. The controller may generate a command signal based onthe field current adjustment.

FIG. 4B illustrates an example circuit for driving the field current.The source 21 may be an exciter generator, a battery, a brush system, orany primary source of current for the field winding. The switch 23 iscontrolled by the controller to increase or decrease the field windingcurrent. In one example, the switch 23 is controlled according to apulse width modulated signal having a duty cycle. The duty cycle isrelated (e.g., proportional) to the intended field winding current. Thefield windings may be modeled by resistive component 25 and inductivecomponent 27. The primary part of resistive component 25 and inductivecomponent 27 is based on the physical wires and connections that make upthe field windings.

However, the stator also acts as source for the field windings. Thearmature reaction source 29 represents the mutual inductance from thestator to the field windings. The armature reaction source 29 alsochanges the inductive component 27 because the inductance of the fieldwindings is changed by the mutual inductance with the stator windings. Asensor or the controller monitors the change in current on the fieldwindings or the change in the inductive component.

FIG. 5A represents a transient response of the field current withrespect to the output current; in the example, the field current is notadjusted in response to changes caused by the mutual inductance with thestator. FIG. 5B represents a transient response of the field currentwith respect to the output current voltage in the example that the fieldcurrent is adjusted in response to changes caused by the mutualinductance with the stator.

FIG. 5A illustrates an example in which the field current is beingcontrolled at a predetermined low level. The field current experiences asubstantially instantaneous increase near T₁ to a much higher level.This increase is caused by an increase in load. Thus, the field currentshould be controlled higher. However, a controller (e.g., voltageregulator) that is controlling the field current to a predetermined lowlevel, has not received any indication that the field current should becontrolled higher. Therefore, the controller causes the field current todecay over time toward the predetermined low level, as illustrated inFIG. 5A. Eventually, the increased load may be communicated to thecontroller, which may increase the field current. However, this sequencerequires significant time (e.g., at least one cycle or the time periodfor a new root mean square (RMS) value to be calculated for input intothe voltage regulator). The detection and correction applied at theregulator, or rotor controller, may achieve a response time that is lessthat one electrical cycle of the alternator output voltage. In oneexample, the response time may be 100-1000 milliseconds.

FIG. 5B illustrates an example in which the field current can quicklyadjust to load changes. When the load on the generator increases at timeT₁, the controller receives an indication immediately. The indicator maybe a sensor signal indicative of a change in current, voltage, orinductance and the field current that has been caused by the change incurrent of the stator windings. The controller immediately responds byadjusting the target field current. The field current is adjusted toreach the target current, as shown by FIG. 5B. Thus, the field currentafter T₁ is higher and closer to the target current in the example ofFIG. 5B. The example of FIG. 5A tends to cause the field current to godown after the increased load, and the example of FIG. 5B tends to causethe field current to go up after the increased load.

A relationship between the current spike at T₁ and the target currentmay be a function of the flux linkage or the coupling factor in Equation1 above. A unity coupling factor may not exhibit an initial change involtage after the application of a load. The removal of a load behavesin a similar manner and may also be detectable by a sudden change in thefield current.

Various types of generators may be used with the examples describedherein. In one example, a brush-type generator supplies current to thefield windings through brushes in contact with slip rings that rotatewith the rotor. In this example, the current of the field windings maybe detected on the rotor. The field current may be adjusted on the rotoror the field current adjustment may be communicated from the rotor backto the stator to adjust the source for the field windings.Alternatively, the stator current may be measured (FIG. 3B), and thefield current adjustment is made at the source. In one example, theimpedance of the field winding is measured through the brush.

In another example, the generator is a brushless generator, as shown inFIGS. 1 and 2. The brushless generator includes an exciter armature thatrotates at the same speed with a common shaft with the rotor of the maingenerator. The field current is generated from the exciter armature; asthe exciter armature rotates voltage in its coils is induced fromexciter windings or permanent magnets. The sensor for detecting thefield current response may be rotating with the exciter. The activatorcomponent may include the control and the sensor.

FIG. 6 illustrates an example of a synchronous generator with apermanent magnet exciter. The synchronous generator includes statorcommunication portion 31, a rotor communication portion 32, exciterfield magnets 33, stator main windings 35, field windings 36, load 37,shaft 39, activator 40 (rotor controller), and voltage regulator 50(stator controller). Additional, different, or fewer components may beincluded.

The activator 40 may include the sensor 41 and controller 43 describedabove for detecting and monitoring the field windings 36 in response tothe current changes in the stator windings 35 from changes in the load37. To adjust the field current the controller may adjust the currentflowing from the exciter to the field windings.

The sensor 41 detects a change in an electrical characteristic of afield winding of an alternator. In one example, the sensor 41 is avoltage detection circuit or current detection circuit. In one example,a single device acts as the controller 43 and the sensor 41. That is aninput signal to the controller describes the electrical characteristicsof the field winding. The sensor 41 may also include a position sensor,a magnetic field sensor, a temperature sensor, a displacement sensorproximity sensor, a deflection sensor or an acceleration sensor.

The controller 43 may adjust a target field setting based on the changein the electrical characteristic of the field winding and generate adriving value for the field winding based on the target field setting.

In another example, the change in the stator main windings 35 isdetected by the voltage regulator 50 and communicated through statorcommunication portion 31 to the rotor communication portion 32 using aphoto-transistor and light source, magnetic communication, or usinganother method. The controller adjusts the field current in response tothe signal from the voltage regulator 50. In yet another example, thevoltage regulator 50 resides on the rotating controller 40 and thestator voltage is passed across the communication interface by magnetic,optical or radio communication.

FIGS. 7 and 8 illustrate example responses of the above examples. Thewound field line illustrates the change in the field current, when thevoltage regulator controls the amplitude of the exciter field, drivingthe voltage on the exciter armature and feeding the main field throughan uncontrolled rectifier. The response 1 line represents an exampleresponse time for adjusting the field current when the voltage regulatormonitors engine speed and alternator output. The response 2 linerepresents the response time when the change in load is detected throughthe mutual inductance on the field windings in the examples above. Thetime delay (TD₂) for response 2 is significantly smaller than the timedelay state (TD₁) for response 1. Example times for TD₂ may be 10-50milliseconds.

The voltage dip for response 1 (VD1) is much more significant than thevoltage dip for Response 2 (VD2) because the rotor controller appliesvoltage to the field much more quickly for Response 2, allowing thefield current to increase more quickly. Similarly, the voltage overshootfor response 1 is significantly higher than the voltage overshoot forresponse 2 because the voltage driving the increase in field current isremoved much more quickly. A typical voltage regulator response(response 1) time may be around 1-5 milliseconds (e.g., 3 milliseconds),while the change in load detection through mutual inductance (response2) may be a magnitude less (e.g., in the range of 50-500 microseconds,or close to 100 microseconds).

FIG. 9A illustrates another example generator. The generator includes astator 60 including multiple windings 61 and a rotor 62 with rotorwindings 63. The stator 60 and the rotor 62 may be an exciter portion ofthe generator or an alternator portion of the generator. Portions areomitted for ease of illustration. In three phase applications, thewindings may be divided into a set for each phase. For example, FIG. 9Aillustrates the windings for phase A, the windings for phase B, and thewindings for phase C. In the three phase application, the phases cancelout because the windings are evenly distributed. That is, as the rotorturns, the magnets 63 are consistently coming into the vicinity of onecoil and leaving the vicinity of another coil. Accordingly, the mutualinductance imputed on the rotor from the stator stays relativelyconstant. In addition, the impact on the current in the field windingsstays relatively constant. The term relatively constant may mean withina predetermined range (e.g., 1%, 10, or 20%).

However, in single phase applications, as shown by FIG. 9B, there isempty space between stator windings 65. This causes the rotor windings63 to come in phase with the stator windings 65 and subsequently passout of phase with the stator windings 65. Thus, a rotor in single phaseapplications does not consistently line up with the stator windings 65.There is a time when magnetic fields in the stator windings 65, butexert no (or very little) influence over the magnetic fields in the mainrotor windings 63. Instead, the magnetic field pass through the air gapbetween poles, or when the stator winding 65 is halfway between twopoles, it affects the two poles similarly, which cancels out.

Because of this phenomenon, the armature reaction, or the component ofmutual flux on the rotor 62 from the stator 60, is variable. Thearmature reaction may reach a maximum value when the stator windings 65are lined up with the rotor windings 63. The armature reaction incidenton the main rotor windings may reach a minimum value when the rotorwindings 63 are halfway between the stator windings 65. Because there istwo maximum values and two minimum values for between each pair ofstator windings 65, the field current may oscillate at twice thefrequency of the output of the generator. For example, on a 60 Hzgenerator, the field current may oscillate at 120 Hz. The armaturereaction varies based on the position of the rotor 62. So the current inthe field windings is dependent on the phase of the rotor.

FIG. 10 illustrates a plot 70 for a field current in the single phaseoperation of the rotor in which the field current frequency is twicethat of the output of the generator and the period is ½ the length ofthe period (T) of the output of the generator. When the rotor (e.g., the4-pole rotor of FIG. 9) is in line with the single phase winding, thearmature reaction has a maximum effect on the field current. When therotor is 45 degrees separated, the armature reaction has a minimumeffect on the field current.

The rotor controller 43 may adjust the load detection algorithm. Therotor controller 43 may measure the field current when there is fullload on the output of the stator. The rotor controller 43 may generate afield current profile based on the full load measurements. The fieldcurrent profile describes the oscillation of the phase current caused bythe relative locations of the stator windings in the single phasealternator. The field current profile may include a series of currentvalues. In one example, the field current profile may be scaled values(e.g., absolute values scaled from 0 to 1, or a ratio of absolute valuesto the average field current or a root mean squared value for the fieldcurrent).

The rotor controller 43 may subsequently detect the field current when aload is placed on the alternator. The rotor controller 43 may access thefield current profile and adjust the measured values for the fieldcurrent according to the field current. In one example, the measuredvalue is adjusted by the field current profile. The value in the fieldcurrent profile may be added to or subtracted from the measured value.For example, at time T₁, the field current profile is at 1 amp. At thatsame T1 in a later cycle, a value of 2 amps is measured. The rotorcontroller 43 may subtract 1 amp from the field current profile from themeasured 2 amp value to calculate a corrected field current.

The rotor controller 43 may calculate a load on the stator from thecorrected field current. The rotor controller 43 may query a lookuptable that associates field current with generator load. Multiple lookuptables may be used or values scaled based on model number, manufacturer,or physical characteristics. The lookup table may include a thresholdvalue for the electrical characteristic of the alternator for multiplealternator models, manufacturers, or types. The regulator (or statorcontroller) may access the lookup table using the model, manufacturer ortype and receive a threshold value for the change in electricalcharacteristic. The rotor controller 43 may calculate other electricalparameters such as output voltage, output current, output power, orother values.

The rotor controller 43 may calculate an adjustment for the fieldcurrent based on the field current profile. The field current may beadjusted to counter the field current profile. For example, the fieldcurrent is increased when values of the field current profile are lowerthan an average value and the field current is decreased when values ofthe field current profile are higher than the average value.

In another example, the field current profile may be used in a threephase application when only one phase is connected to a load. Forexample, when a three phase application has outputs A, B, and C, theremay be no load coupled to phases B and C. Thus, phase A performs similarto a single phase application.

The generator may include a rotating exciter. Rotating exciters mayinclude permanent magnets on the stator side of the generator androtating coils on the rotor side of the generator. The stator coreincludes iron (e.g., steel), which has a high magnetic permeability. Thehigh magnetic permeability causes an inductive component (e.g.,reactance) in the current generated on the rotating exciter. Theinductive component causes a voltage drop across the exciter windings. Areduction in the iron of the core leads to less of a voltage drop andaccordingly, increases the efficiency of the generator.

In one example, the exciter windings are provided by a printed circuitboard (PCB) or PCB assembly. FIG. 11 illustrates an example rotorcontroller in a synchronous generator including stator communicationportion 31, a rotor communication portion 32, stator main windings 35,field windings 36, load 37, shaft 39, a PCB assembly 40, a stator core51, stator magnets 53, and a stator controller 50. Additional,different, or fewer components may be included.

The PCB assembly 40 may include circuitry and other electricalcomponents for a rotor controller 43, a sensor 41, and a communicationdevice 45. The PCB assembly 40 may include exciter windings 54 arrangedradially out from the shaft 39. The exciter windings 54 may be coils ofwire coupled to the PCB assembly 40. The exciter windings 54 may bewindings or traces between two layers of PCB.

Integration of the exciter windings 54 and the PCB assembly 40 achievesseveral advantages. Because the exciter windings are integrated with thePCB assembly 40, the stator core 51 that supports the stator magnets 53is moved to the plane in parallel with the plane of rotation of the PCBassembly 40. For example, the circuit board may contain traces arrangedin concentric circles constituting coils to provide power to control thefield current. The traces may also exist on multiple layers within theboard and may be connected in series, parallel, or a combination ofseries and parallel. The board may include terminals to connect one ormore wires to the printed circuit board. The wires may attach tosensors, transducers, switches the rotor field winding or other devicescontrolling an electrical characteristic of the rotor.

Because the armature traces reside on the printed circuit board, thearmature reactance (caused by the permeability of the iron used todirect the magnetic flux through the windings) is much lower, decreasingthe voltage drop under load and improving the efficiency of thegenerator. Less steel is used in the magnetic flux path for thisarrangement. A reduction in steel means less reactance to cause avoltage drop across the exciter windings, which improves the efficiencyof the generator. In addition, lower reactance of the exciter armaturemay decrease the switching time and switching losses in SCR switches ordiodes used to control the rotor field current and serves to decreaseinductive voltage spikes applied to an insulated-gate bipolar transistor(IGBT) or field effect transistor (FET) switches used to control therotor field current.

In addition, the size of the generator may be reduced. The magnets,which are normally spaced radially around the exciter armature, aremoved to be parallel to the plane of rotation of the exciter armature,as illustrated by FIG. 11. Thus, the exciter portion of the generator isgreatly reduced in size, such as a decrease in the overall length of thealternator. Accordingly, the generator may be installed in a smallersize (e.g., smaller footprint), and storage and shipping costs arereduced.

FIG. 12 illustrates an example construction of the PCB assembly 40. ThePCB assembly may include a circuit board 57 separated from the exciterwindings 54. The circuit board 57 may include the rotor controller 43,the sensor 41, one or more switches 47 to control the field current, andthe communication device 45. The circuit board 57 may be physicallyspaced from the exciter windings. For example, a non-conductive spacer(e.g., rubber or plastic) may be mounted between the circuit board 57and the exciter windings 54. The non-conductive spacer may include oneor more through holes for passing wires or conductive leads from thecircuit board 57 to the exciter windings 54.

FIG. 13 illustrates another example rotor controller. In the example ofFIG. 13, potential design alternatives are shown. For example, themagnets 53 may be omitted from the stator on one side of the PCBassembly 40. The iron in the other side of the PCB assembly may providea path to complete the magnetic flux path for the flux produced by thepermanent magnets. The magnetic flux may continue to flow though theboard in a similar fashion with magnets 53 on a single side of the PCB.In addition, the magnets 53 may be placed such that only the magnets 53oriented in a given direction (i.e., north, south) are included and theflux is directed through the PCB using the iron around the magnets 53.

In addition, the corresponding one or more stator magnets 53 may also beomitted. Thus, magnetic flux may flow in FIG. 13 from the from thestator magnets 53 on the left side of the PCB assembly 40 through theexciter windings 54 and to the stator core 51 on the right side of thePCB assembly.

FIG. 14 illustrates another example rotor controller. In the example ofFIG. 14, the stator magnets 53 may be replaced with coils 55. As shown,coils 55 are used on both sides of the PCB assembly 40. In oneimplementation, coils 55 are used on one side of the PCB assembly 40 andstator magnets 53 are used on the other side of the PCB assembly 40.Less stator coil 41 material may be used with these implementations.

Another advantage realized with the stator magnets 53 or stator coils 55are located in the plane parallel to the plane of rotation of theexciter or PCB assembly 40 is that a risk of complications with thepower electronics due to switch shorting in the diodes is reduced.Switch shorting occurs when an inductive source is commutated into aload using a single-directional device (such as a diode or an SCR). Thecurrent flowing into the inductive load will continue to flow from agiven source output until the current through the inductance of thesource decays to 0, but the current will start flowing through adifferent path as it decays, resulting in a short-circuit on the outputof the source until the switching occurs.

FIG. 15 illustrates a stator 130 and an exciter armature 135. The stator130 includes an arrangement of irregularly spaced stator magnets 131.The illustrated example includes ten magnets of alternating polarity,but any number or any even number of magnets may be used. The exciterarmature 135 includes a pickup coil 133, in addition to the othercomponents discussed herein, including the coils for generating thecurrent that supplied a DC bias to the field windings of the rotor. Amajority of the magnets are spaced at a first interval W₁. At least onepair of the magnets are spaced at a second interval W₂. The secondinterval may be substantially greater (e.g., 2 times, 3 times, or more)or substantially less than (e.g., ½, ⅓ or another fractional amount) thefirst interval. In the example of FIG. 15, the second interval is atleast three times the first interval. A pickup coil 133 on the exciterarmature rotates within the ring of stator magnets 131. The pickup coil133 detects the magnetic flux of the passing magnets and identifies arotation position of the second interval in the stator magnets.

The pickup coil 133 may be a wire or trace on a circuit board (e.g., PCBassembly 40). As the stator magnets 131 pass the pickup coil 133, themagnetic field in the vicinity of the pickup coil 133 is disrupted,which causes a current to be induced in the pickup coil 133. The pickupcoil 133 is connected to a controller (e.g., controller 43), whichmonitors the current in the pickup coil 133.

FIG. 16 illustrates an example plot current in the pickup coil 133. Anoutput portion 138 of the plot illustrates three phases of the output ofthe generator. The output portion 138 may be an AC waveform of theoutput of the alternator, which may have multiple components or phases,which may voltage AB, voltage BC, and voltage CA. A pickup coil portion139 of the plot illustrates the output of the pickup coil 133. Thepickup coil output is sinusoidal and a substantially constant period asthe pickup coil 133 passes the regularly spaced magnets spaced apart bythe first interval W₁. When the pickup coil 133 passes the irregularlyspaced magnets and the second interval W₂, the sinusoidal pattern isdisrupted.

The disruption of the sinusoidal pattern may be detected by the rotorcontroller 43. The output of the pickup coil 133 may be a trigger signalthat is triggered when the irregular space or home position passes thepickup coil 133. A communication interface may receive the triggersignal from the pickup coil 133. The rotor controller 43 may detect thetrigger signal from the pickup coil 133 of based on output voltages,output currents, output power, or output timing. The rotor controller 43may monitor the output of the pickup coil 133.

In one example, the rotor controller 43 compares a period of the outputof the pickup coil 133 to a threshold period. The threshold period maybe passed on the first interval W₁. When the period of the output of thepickup coil 133 exceeds the threshold period, the rotor controller 133determines that the irregularly spaced magnets have been passed or thatthe rotor is at a home position. The home position may be any particularangle, and the rotor controller 43 makes calculations based on the homeposition. In one example, the rotor controller 43 compares the outputvoltage from the pickup coil 133 to a threshold. When a peak of theoutput voltage from the pickup coil falls below the threshold for apreset amount of time, the rotor controller 43 identifies that theirregularly spaced magnets have been passed or that the rotor is at thehome position.

The communication interface or the rotor controller 43 may receive dataindicative of an output of the generator. The rotor controller 43performs a phase analysis of the trigger signal and the output of thegenerator. The rotor controller 43 may determine when the output of aparticular phase crosses a predetermined output level (e.g., 0 volts).The rotor controller 43 compares the time when the particular phasecrosses the predetermined output level to the time when the output ofthe pickup coil 133 is at the home position.

The rotor controller 43 may calculate a power angle for the generatorbased on the phase analysis. The power angle may be the phase differencebetween the output of the pickup coil 133 and the output of thegenerator. The power angle is the angle between the rotating magneticflux in stator and rotating magnetic flux in the output.

In one example, the rotor controller 43 queries a lookup table with thepower angle for the generator and receive a power value from the lookuptable. The lookup table may be stored in a memory coupled to orintegrated with the rotor controller 43. The lookup table may betailored to a particular model of generator or alternator, a particularmanufacturer of generator or alternator, or a particular type ofgenerator or alternator. The lookup table may be created based ontesting. That is, the lookup table may be created from measured powerangles for known output levels.

When there is no load on the generator the delta is zero because therotating magnetic flux in stator and rotating magnetic flux are in line.As more power is provided to the load, there is a torque on the engine,and the angular distance between the rotor and stator increases. Thelookup table may associate the power angle to one or more electricalparameters such as output power. The lookup table may extend from 0 to amaximum number of degrees. The maximum may depend on the particulargenerator. Example maximums may be 20 to 30 degrees.

The power value may be indicative of an output of the generator or theexciter based on the power angle. The rotor controller 43 may comparethe power value to one or more threshold values. One threshold value maybe indicative of an error condition of the generator. For example, thegenerator is experiencing a malfunction which causes the power angle todeviate from an expected value. In response, the rotor controller 43 maygenerate a safety signal in response to the power value exceeding thethreshold level. The rotor controller 43, or stator controller 50, mayperform a function in response to the safety signal. The function maycut the power supply to the field windings. The function may turn offthe engine that drives the rotor.

The rotor controller 43 may modify the output of the exciter or theoutput of the generator. For example, the rotor controller 43 maycontrol the output of the exciter based on a target value. When thepower value exceeds the threshold level, the rotor controller 43 maymodify a target value for the generator in response to the power valueexceeding the threshold level.

The rotor controller 43 may perform load balancing in response to thepower value exceeding the threshold value. The rotor controller 43 maygenerate a load balance signal in response to the power value exceedingthe threshold level. The load balance signal may be sent to the statorcontroller 50 or a system controller for a set of parallel generators.The stator controller 50 or the system controller may adjust the outputof the generators in order to equalize or configure the load among thegenerators. In one example, the loads are balanced across generators byincreasing or decreasing the rate that fuel is supplied to the engines.The fuel adjustment may change the real power supplied by thegenerators. In one example, the loads are balanced among generators bymodifying the current levels supplied to the alternator field windings.

The rotor controller 43 may perform a paralleling function in responseto the power value exceeding the threshold value. For example, when theload is above a threshold the rotor controller 43 or stator controller50 may generate a paralleling signal in response to the power valueexceeding the threshold level. The paralleling signal may include aninstruction to bring an additional generator online. The instruction maycause a generator to close to the bus or begin running. The parallelingsignal may include a time value in order to synchronize the generators.

The rotor controller 43 may perform a load shedding function in responseto the power value exceeding the threshold value. The rotor controller43 may generate a command for a switch that adds or removes a load fromthe generator. When the power angle is too high, loads may be removed.When the power angle is low, loads may be added.

The rotor controller 43 may generate any of these commands in responseto the power value exceeding the threshold value. The rotor controller43 may send the command to the stator controller 50. The size of thepower angle may impact whether the resulting function is performed atthe rotor controller 43 or sent to the stator controller 50.

The rotor controller 43 may cooperate with the stator controller 50 in amaster and slave relationship. For example, in a first mode the statorcontroller 50 performs a majority of the control functions of thegenerator and in a second mode the rotor controller 43 performs amajority of the control functions of the generator. The rotor controller43 may initially be in the slave role, providing data to the statorcontroller 50. When the rotor controller 43 sends a command or otherdata to the stator controller 50, the rotor controller 43 may start atimer. If the timer reaches a predetermined level (e.g., 1 second, 10seconds, or another value) without a response or acknowledgement beingreceived from the stator controller, the rotor controller 43 may takethe role of the master. That is, the rotor controller 43 may startingapplying generator commands without any involvement from the statorcontroller 43.

The rotor controller 43 may calculate electrical parameters of theoutput of the generator based on the power angle. The electricalparameters may include current, voltage, or power for one or more phasesof the output. The electrical parameters are calculated without the useof a current transformer. This is advantageous because currenttransformers may be eliminated from the generator, which reduces cost.In addition, this technique is less time consuming that currenttransformers because no calibration is needed. However, it is noted thata calibration based on manufacturing variances between alternators maybe applied, but no calibration based on temperature or load isnecessary.

FIG. 17 illustrates another implementation for the PCB assembly 40including the exciter armature 135 and a control portion 134 with sensor41, controller 43, one or more switches 47, and communication interface45. The example illustrated in FIG. 17 rotates in a plane neartwenty-four magnets mounted on the stator 130. The magnets aredesignated near coils 131 with indicators 132, using N for north and Sfor south. The magnets are mounted to stator 130, which may be in frontof the PCB assembly 40 shown in FIG. 17. In other words, the PCBassembly 40 and coils 131 move relative to the magnets illustrated byindicators 132. The magnets 131 may be spaced at a first distance.However, between at least one pair of magnets 131, a second distance(W₂) separates the magnets. The one or more switches 47 turn on and offthe field current in the windings of the exciter armature 135. Theswitches 47 may be driven by a control signal from the controller 43(e.g., a pulse width signal).

FIG. 18 illustrates another implementation for the stator 130, which isshown only by magnet indicators 132, which are either behind or in frontof the PCB assembly 40 including the exciter armature 135 and a controlportion 134 with sensor 41, controller 43, one or more switches, andcommunication interface 45. FIG. 18 illustrates the case where theposition of the rotor is detected by measuring an irregularity in theiron in the stator surrounding the PCB assembly 40. The change in themagnetic path length for the field generated in the pickup coil 71 bythe current source 73 results in a voltage that can be detected by avoltage sensor 75. The position sensor detects when the rotor is at acertain position and the relative position of the rotor can be obtainedby counting cycles on the voltage generated on the outer turns, or bycomparing the incoming voltage to a threshold or series of thresholds.

Any arrangement may be used in which the home position can be markedusing the magnets. In addition to irregular spacing, changes insequence, an odd number of magnets, different sized magnets may be used.For example a magnet may be replaced with two smaller magnets, resultingtwo shorter cycles in the output of the pickup coil 133. The magnetsillustrated are arranged in a pattern of alternating north (N) and south(S) poles (e.g., NSNSNSNSNSNSNS). However, the home position may bemarked by a repeating pole of the same polarity (e.g., NSNSNSNNSSNSNS orNSNSNSSSNSNS).

FIG. 19 includes a flowchart for calculating electrical parameters fromthe detected power angle, which may be implemented by any of thearrangements (e.g., FIG. 14 or FIG. 16). Additional, different, of feweracts may be included.

At act S201, the alternator controller 43 receives a trigger signal fora position of the rotor. The alternator controller 43 may consult alookup table to determine an expected position of the rotor based on thetrigger signal. Alternatively, the trigger signal may be associated witha home position. The home position may be the initial tooth (tooth 1) ofa gear that drives the rotor.

At act S203, the alternator controller 43 detects a zero crossing of theoutput of the alternator. The output of the alternator may be calculatedat the rotor controller 43 according to any of the examples describedherein for calculating load, output current, output voltage, or outputpower.

At act S205, the alternator controller 43 determines the power angle.The power angle may be calculated based on a difference between ameasured zero crossing time and an expected zero crossing time. Theexpected zero crossing time may be based on the number of phases of theoutput and a number of stator magnets for the generator. The generatorwith M phases and N stator magnets. Each stator magnet is reflected ineach of M phases in the output of the exciter. Thus, there are N×M(product of N and M) zero crossings in the output of the exciter forevery rotation of the rotor. For example, with three phases and tenstator magnets spaced N-S alternately, there are 30 zero crossings foreach revolution or each period in the output.

At act S207, the alternator controller 43 queries an output table for agenerator parameter. The output table may associate power angles with avalue indicative of the output of the generator, the load on thegenerator, or another generator parameter. The difference between therotating fields of the rotor and stator is changed depending on thegenerator parameter. As the load on the generator increases, the powerangle increases.

At act S209, the alternator controller 43 generates command based on thegenerator parameter. The command may be any of the functions describedherein including a safety shutdown when output power goes past athreshold level, an adjustment to a target frequency or voltage toprotect something, generator paralleling functions, load balancingfunctions, or load shedding functions. The command may be sent toanother controller such as the stator controller 50.

FIG. 20 illustrates an example in which the position of the rotor isdetected using a pickup coil 136, mounted on the rotor and a permanentmagnet 132 on the stator 130. The permanent magnet 132 on the stator maybe mounted at a different radius than the magnets that supply the fieldexcitation voltage. The permanent magnet may be the same permanentmagnets used for generating the excitation voltage for the rotor, or itmay be a separate magnet. The pickup coil 136 may also be mounted at adifferent radius than the coils that supply power to the rotor. Thepickup coil may also have a built-in permanent magnet or a currentimpressed on the coil so that an irregularity (such as a bump or dip orgear tooth) can be detected by the pickup coil. The output of the pickupcoil 133 may be analyzed according to any of the examples herein. FIG.20 illustrates the magnets of the stator out of phase with the coil 101as the PCB assembly rotates with respect to the stator.

When a non-linear load or device is activated on the load side orcustomer side of a device or circuit connected the output of agenerator, the field current may be affected. An example of a non-linearload that causes such a disruption is a silicon controlled rectifier(SCR). The non-linear load may operate as a high speed switch. Othernon-linear loads may include power factor correction devices,insulated-gate bipolar transistors (IGBTs), or capacitive buses. When astate of the non-linear load or device is changed or switched, amagnetic flux may be induced on the load side of the stator, whichcauses a mutual inductance to be applied to the rotor windings, changingthe field current.

The rotor controller 43 may detect the change in the output of thestator. Consider the example in which the controller is monitoringfrequency by identifying when the output crosses zero. The frequency ofthe output may be calculated as proportional to the number of zerocrossings in a time period. For example, one crossing in the time periodmay indicate 60 Hz, two crossings in the time period may indicate 120Hz, and three crossings in the time period may indicate 180 Hz.

FIG. 21A illustrates a sinusoid disrupted by two spikes caused by thenon-linear loads. The spikes may occur at the same point in time withinthe cycle or every half cycle. If the output was sinusoidal without thespikes, the controller detects one zero crossing (e.g., corresponding to60 Hz). If the non-linear load causes the spikes shown, the controllerdetects two more zero crossings (e.g., 3 total crossings, correspondingto 180 Hz).

The rotor controller 43 may detect the occurrence of these spikes fromthe mutual inductance induced on the rotor. For example, the rotorcontroller 43 may monitor the field current and determined when there isa spike (e.g., threshold change in voltage or current over a short timeperiod). In one example, the rotor controller 43 may count the number ofspikes and generate a signal or message indicative of the number ofspikes.

In one example, the rotor controller 43 detects the zero crossing andthe spikes. In another example, the rotor controller 43 detects thespikes and communicates the information to the stator controller 50,which detects the zero crossings.

The controller (e.g., either rotor controller 43 or stator controller50) that monitors the output of the stator may adjust the detectedfrequency based on the number of spikes detected based on mutualinductance. The number of spikes corresponds to the number of “extra” or“false” zero crossings shown in FIG. 21. For example, the controller maycalculate the number of zero crossings, subtract the number of detectedspikes, and calculate a frequency of the output of the stator based onthe result. FIG. 21B illustrates a flowchart for calculating a frequencyof the output of the stator corrected by the number of disturbances.

As a result of the clean frequency detection, the over frequency is“ignored” and the generator is not shut down when the high frequency iscaused by the spikes from the non-linear load. In one example, thecontroller may generate a message for a display or interface of thegenerator that states that a non-linear load is present. Alternatively,the message may indicate the updated frequency measurement.

The rotor controller 43 may calculate an impedance of the alternator.The stator controller identifies spikes in the stator output caused bynon-linear loads. The magnitude of the spike is related to the sourceimpendence of the alternator. The rotor controller 43 may identify amaximum magnitude of the change in output caused by the spike. Examplesfor the maximum magnitude of the change include 10%, 20% or anothervalue.

When the non-linear load causes a change in output that exceeds themaximum magnitude, the rotor controller 43 may generate a warning or acommand. The warning may inform the user that excessive non-linear loadsare on the generator. The warning may be displayed on a display or userpanel for the generator. The warning may be sent to a mobile device(e.g., laptop or cellular phone). The warning may be sent to amanufacturer or manufacturer's representative in order to log theinstance for maintenance purposes.

The rotor controller 43 may be configured to identify patterns in thenon-linear load. For example, the rotor controller 43 may record atimestamp each time an unexpected spike or zero crossing occurs in thestator input. The rotor controller 43 may identify that a specific timeperiod has elapsed between spikes or between a statistically significantnumber of pairs of spikes or sequential pairs of spikes.

For example, the rotor controller 43 may record timestamps for a minimumset number (e.g., 10, 20, 100 or another value) of samples. The rotorcontroller 43 may calculate differences of sequential pairs (e.g., the2^(nd) timestamp minus the 1^(st) timestamp or the 11^(th) time stampminus the 10^(th) timestamp). Alternatively, the rotor controller 43 maycalculate differences between every other sample (e.g., the 4thtimestamp minus the 2nd timestamp or the 11^(th) time stamp minus the9^(th) timestamp). The rotor controller 43 may perform a statisticalanalysis on the timestamp differences to determine whether a regularpattern has been occurring. In one example, the rotor controller 43 maycalculate a standard deviation of the differences. When the standarddeviation is within a threshold value, the rotor controller 43determines that a pattern has been identified.

Once the pattern has been identified, the rotor controller 43 isconfigured to adjust the field current to account for the spike. Therotor controller 43 may determine expected times for the non-linearload. For example, the rotor controller 43 may anticipate the firingtime for an SCR. At the predicted time of the non-linear load, or thetime just before the predicted time of the non-linear load, the rotorcontroller 43 may increase the field current.

The increase in field current may be brief in time and high inmagnitude. To achieve these levels, an energy storage device capable ofquick charging and discharging (such as a capacitor or an inductor) maybe used. The rotor controller 43, in response to the predicted time inthe pattern, may activate a switch that connects a charged capacitor toone or more of the field windings. Examples sizes for the capacitorinclude 0.1 uF to 10 uF at 3000 VDC or 1 to 100 uF at 1000 VDC. Examplesizes for the inductor include 1 mH to 100 mH at 15 A.

The rotor controller 43 may analyze the total harmonic distortion (THD)spike caused by the non-linear load. The rotor controller 43 mayidentify a first period of time when the non-linear load is present anda second period of time when the non-linear load is not present. Therotor controller 43 may measure THD during the first period of time as abaseline. The rotor controller 43 may measure THD during the secondperiod of time. The THD may be the ratio of a ratio of the power densityof a range of harmonics to the power density of the fundamentalfrequency to the fundamental frequency. Based on a comparison of themeasurements, the rotor controller 43 calculated how much THD is causedby the non-linear load.

Based on the THD levels, the field current may be controlled accordingto a field control profile, which is discussed in more detail in theexample below and in association with FIGS. 25A-B and 26. In oneexample, the rotor controller 43 may generate a user message in responseto the THD. The user message may inform the user that a non-linear loadis causing THD and/or engine speed changes are introducing flicker intothe field current profile.

In one technique, the current in the stator is detected using currenttransformers (CTs). The current transformers are inductive sensors thatattach to the outside of the generator leads. The stator controller 50receives the output of the CTs as a current measurement. The controllermultiplies the current measurement by a voltage measurement to calculatepower. However, CTs have a few downsides. CTs are expensive, add adegree on non-linearity to the current measurement, and are hard toconnect because the wiring depends on the alternator connectionconfiguration. In addition, CTs are easily installed incorrectly becausethe generator often has many leads, and three phase connections may beconfusing. CTs must be mounted by brackets and individual wiringcalculations are made. This takes time and has high labor costs.

The rotor controller 43 is configured to calculate the power without thecurrent measurement and without the CTs. Individual power components(e.g., real power, reactive power, instantaneous per phase power andapparent current) may be calculated without directly measuring thestator current level.

FIG. 23 illustrates an example flowchart for calculating stator current.From the stator current the output power and power currents may becalculated. Additional, different, or fewer acts may be included. Someor all of the acts may be performed by the rotor controller 43.

At act S301, the alternator speed or synchronous speed (n_(s)) ismeasured. The speed may be measured based on the irregularly spacedmagnets and techniques described herein in association with FIGS. 15-17.The speed may be based on time between markers for the home position.For example, the time between markers divided into one minute gives thesynchronous speeds in revolutions per minute. Other speed calculationsare possible.

At act S303, the field current is measured. The field current may bemeasured directly by the rotor controller 43. One example technique formeasuring field current is shown in FIG. 4A and described herein. Therotor controller 43 may set the field current. One example technique foradjusting a field current setting is shown in FIG. 4B and describedherein.

At act S305, the rotor controller 43 calculates an excitation voltage asa function of field current and alternator speed. Equation 2 illustratesan example calculation, and variations are possible. The excitationvoltage E_(f) in volts may be calculated according to:

$\begin{matrix}{E_{f} = {n_{s}\frac{N_{f}I_{f}}{R}k_{f}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

The synchronous speed (n_(s)) (e.g., revolutions/minute) may be measuredby the pickup coil 133 or other techniques in at S301. The DC fieldcurrent (I_(f)) may be measured by the rotor controller in act S303.

The number of conductor turns N_(f) is a property of the field coil.This may be a known value based on the alternator that is stored inmemory by the alternator controller 43. Alternatively, the rotorcontroller 43 may consult a lookup table that associates alternatormodels with the number of conductor turns. In another example, thenumber of conductor turns may be calculated from a resistancemeasurement In another example, resistance is detected and the number ofturns is calculated based on the gauge of wire and the relationship ofresistance and inductance as the relationship changes over temperatureranges.

The term k_(f) is a constant representing magnetic coupling efficiencyor leakage flux. This value may be stored in memory and accessed by therotor controller 43. Alternatively, this value may be measured usingknown armature currents and a variable known load. The term R is thereluctance of the magnetic circuit (e.g., ampere—turns/weber,turns/henry), which is effectively a constant.

In one alternative, the constants may be collapsed to a single value asan alternator constant—A, the excitation voltage is proportional to theDC field current and the speed, as shown by Equation 3.

E _(f) =A I _(f) n _(s)   (3)

At act S307, the rotor controller 43 calculates the stator impedance.Various techniques may be used for this calculation. One of which isshown geometrically by FIGS. 24A-B. FIG. 24A illustrates a vector plotof operation of the synchronous machine. The synchronous machine may bea generator. A first triangle 81 constructed from three vectorquantities, V_(T), E_(f), and I_(a)Z_(s). V_(T) is the output voltage ofthe stator (terminal voltage). E_(f) is calculated from Equation 2 atact S305.

A second triangle 83 is constructed from three vector quantitiesI_(a)/X_(s), I_(a)R_(a), and I_(a)Z_(s). While the direction of thevectors is important in both triangles, an assumption may be made that aclosed triangle is formed is formed from the three vector quantities,allowing the direction of the vectors to be omitted from calculations.

The armature phase current I_(a) is an instantaneous quantity. There arethree time based currents (one for each phase) of the generator. Therotor controller may select a phase based on the position of the rotoras determined by the output of the pickup coil 133.

FIG. 24B illustrates triangle 85 which is congruent and smaller thantriangle 83. Each vector component of triangle 83 has been divided byphase current I_(a) to construct triangle 85. X_(s) is a constant thatdescribes the alternator material properties and design (e.g., number ofturns, magnetic properties of steel, winding ratios, windingdistribution or other factors). This value may be stored in memory andaccessed by the rotor controller 43. Alternatively, this value may bemeasured using known armature currents and a variable known load. Xs mayalso be calculated based on geometric and material information relatingto the alternator design to account for changes in the characteristicsdue to air gap size and permeability (due to saturation of the machine).

R_(a) is another constant that describes the series resistance of thealternator; this is temperature dependent. R_(a) may be calculated orapproximated. R_(a) may calculated based on temperature detected by anambient sensor (e.g., temperature sensor). R_(a) may be calculated basedon a measurement from a search coil that reflects temperature based onelectrical properties. R_(a) may be estimated based on an expectedtemperature. The temperature may be estimated based on load on thegenerator. R_(a) may be a function of the temperature and the load onthe generator. Thus, Z_(s) is based on two known constants for thealternator. Because Ra is the smallest leg of the triangle 805, errorsin R_(a) may be less significant.

Returning to the first triangle 81, with I_(a)Z_(s),V_(T), and the anglebetween them, load angle δ. The load angle is calculated based onrotation of the rotor according to positions of asymmetrical excitermagnets. The load angle or power angle may be calculated according tothe techniques described herein in association with FIGS. 15-18.

The law of cosines may be used to calculate I_(a)Z_(s), for example, asshown in Equation 4. Equation 5 is solved for the phase current. Thus,the phase current I_(a) may be calculated rather than measured using acurrent transformer. The current transformer may be omitted.

$\begin{matrix}{{I_{a}Z_{s}} = \sqrt{V_{T}^{2} + E_{f}^{2} - {2\left( V_{T} \right)\left( E_{f} \right){\cos (\delta)}}}} & {{Eq}.\mspace{14mu} 4} \\{I_{a} = \frac{\sqrt{V_{T}^{2} + E_{f}^{2} - {2\left( V_{T} \right)\left( E_{f} \right){\cos (\delta)}}}}{Z_{s}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

After the armature current is obtained in act S309, several additionaldeterminations may be made by the rotor controller 43 related toalternator temperature, winding irregularities, droop control, interturnshorts, and stationary tests.

The stator temperature may be calculated from the armature (stator)current obtained in act S309. The armature windings and/or the fieldwindings may be formed from a single material (e.g., copper). Thus, thechange in resistance calculated from voltage and current measurements isindicative of temperature. There is a direct relationship betweenresistance and temperature. The rotor controller 43 may access a lookuptable that associates armature temperature from armature resistance anda lookup table that associates rotor temperature with field windingresistance. The lookup tables may be stored in memory. Alternatively,temperature and resistance may be associated via algebraic formulaaccording to a winding material (e.g., copper) constant. In one example,as shown by Equation 6, the new resistance (R_(new)) is related to theprevious resistance (R_(old)), the new temperature (T_(new)), theprevious temperature (T_(old)), and the material constant (T_(k)). Thematerial T_(k) is 234.5 for copper and 225 for aluminum. The temperaturevalues are measured in in degrees C.

R _(new) =R _(old)*(T _(new) +T _(k))/(T _(old) +T _(k))   (6)

The rotor controller 43 may identify winding irregularities based on thearmature current from act S309 and field winding current. For example,the rotor controller 43 may calculate a ratio between armature currentand field winding current. When the ratio deviates from a predeterminedrange, the rotor controller 43 determines that an irregularity hasoccurred. The irregularity may be a turn to turn short. The turn to turnshort may be a short that has occurred between two windings that shouldbe insulated from one another. The rotor controller 43 may identify thatthe short has occurred on the rotor side when the ratio is less thanexpected and the rotor controller 43 may identify that the short hasoccurred on the stator side when the ratio is higher than expected. Inother words, if the rotor current is higher than expected for a givenstator current, the number of turns on the rotor is noticeably low, andif the rotor current is lower than expected, the stator may have a shortcircuit (although the output voltage may decay to the point where therotor current would probably have to go up, not down).

In one example, the winding irregularity may be a short from windings tolaminations. The short may be detected by the rotor controller andhandled with a fault action, such as removing excitation from thealternator or logging an event. A short to the laminations can bedetected by detecting a current path using a technique such as periodichigh-potential detection or a constant voltage applied between the rotorlaminations and the windings.

The rotor controller 43 may perform a self-diagnosis of some problemswhen the errors occur. The rotor controller 43 may monitor theinductance of the field windings. When the inductance changesunexpectedly in comparison to the change in resistance, the rotorcontroller determines that an interturn short has occurred.

In one example, the rotor controller 43 make a series of resistancemeasurements at time intervals and a series of inductance measurementsat the same time intervals. The rotor controller 43 may calculate abaselines ratio of resistance to inductance or inductance to resistance.The resistance and inductance should vary proportionally, if thetemperature of the winding has stabilized. Therefore, for any subsequentmeasurement of resistance, the rotor controller 43 may calculate anexpected inductance, and for any subsequent measurement of inductance,the rotor controller 43 may calculate an expected resistance. When theexpected value for inductance or resistance deviates from the measuredvalue by a predetermined amount, the rotor controller 43 determines thatan interturn short has occurred.

The rotor controller 43 may detect demagnetization of the magnets at theexciter on the stator assembly 610. The rotor controller 43 may measurespeed of the rotor using the pickup coil 133. The speed of the rotor isrelated to the excitation voltage determined at act S305. The rotorcontroller 43 may monitor the excitation voltage and speed. Theexcitation voltage and speed should vary proportionally. Therefore, forany subsequent measurement of excitation voltage, the rotor controller43 may calculate an expected rotor speed, and for any subsequentmeasurement of rotor speed, the rotor controller 43 may calculate anexpected excitation voltage. When the expected value for excitationvoltage or rotor speed deviates from the measured value by apredetermined amount, the rotor controller 43 determines that one ormore magnets have become de-magnetized. The rotor controller 43 maycompare the deviation against multiple thresholds to determine whetherone, two, three, or another number of magnets have become demagnetizedor if the total magnetic flux of the permanent magnets is weakening.

The rotor controller 43 may detect shorts to ground as an alternative tostationary testing. In stationary testing, a high potential (hipot)circuit is used to test the stator or rotor windings for inadvertentshorts to ground. For example, the electrical insulation that insulatesthe windings may become cracked, broken, or worn through, which providesa current path to ground.

The hipot circuit may include a lead that can be connected to ground anda power source that is both high voltage and low current. Under normalconditions, when the power source is connected between the windings andthe rotor shaft no current should flow through the hipot circuit.However, when a current is detected through the hipot circuit above athreshold (e.g., 10 milliamps) is exceed, a failure is detected. AC andDC voltage can be used for hipot testing, but the capacitive couplingbetween the rotor winding and the laminations is often sufficient topermit enough displacement current to pass through the capacitivecoupling, resulting in an inaccurate test result. DC hipot testingeliminates the capacitive path by eliminating maintained displacementcurrent (only charging current is observed).

In rotor hipot testing, the hipot circuit is stationary. Because thehipot circuit must be physically connected to router windings, the rotormust be stationary. To test multiple portions of the rotor, the rotormay be incrementally rotated and the hipot test performed at eachincrement. Often, an error may only be detectable at a certainrotational position (or range of rotational positions) of the rotor.These are referred to as stationary tests.

As an alternative to stationary testing, as shown in example embodimentsincluding FIGS. 1, 5, 11, 13, 14, and 21, the rotor controller 43rotates along with the rotor assembly, and may include a hipot circuitthat detects continuity to ground. The hipot circuit includes groundlead and power source. The ground lead may connect to the shaft 39. Thehigh voltage and low circuit power source is connected to the positiveor negative supply lead for the rotor winding.

The rotor controller 43 may detect a leakage current through the highpot circuit and compare the current to a minimum leakage current.Examples for the minimum hipot current includes 1 milliamp, 5 milliamps,and 10 milliamps. The rotor controller 43 may initiate the testingaccording to a user input or a schedule. The user input may be generatedby a test button or another input on a user interface. The schedule maybe periodically (e.g., every week or month), at specified times, or inresponse to an event. The event may be another error, a startup, or achange in load on the generator.

In response to the detected failure, the rotor controller 43 may log theerror, report the error, or take a corrective measure. The rotorcontroller 43 may log hipot currents and timestamps when the hipotexceeds a threshold. The rotor controller 43 may report the error to theuser via a display on the user interface, a message to a mobile device,or an audible message (e.g., alarm). The rotor controller 43 may reportthe error to the stator controller 50 or generator system controller.The rotor controller 43 may take a corrective measure by shutting downthe generator or reducing the field current. In one example, the hipotfailure may be aggregate with other errors from other testing in thegenerator in an error score. When the aggregate error score exceeds amaximum level, the rotor controller 43 generates a command to turn offthe generator. In one example, the corrective measure or the report ofthe error may indicate that either the rotor windings or stator windingsshould be replaced, repaired or rewound.

Because the rotor controller 43 is integral to the alternator, that is,the rotor controller 43 can take readings, analyze data, and takecorrective measures independent of other logic located outside of thealternator, the alternator may employ protective measures. Because thecontroller is onboard the rotor, the alternator may be able to protectitself without the need for an external device. No external device isneeded to detect problems with the alternator.

The protective measures may include current based protection. The rotorcontroller 43 may detect the field current. One example technique formeasuring field current is shown in FIG. 4A and described herein. Therotor controller 43 may calculate the power dissipated in the fieldwindings over time. Such dissipated power (DP) may be calculatedaccording to Equation 6.

DP=I ² *t   (6)

The DP may be power dissipated in the coil (heat) multiplied by theamount of time that the power is dissipating. The rotor controller 43may compare the DP to a heat threshold to determine when there is anoverheating or a risk of overheating. The rotor controller 43 may alsoaccount for the amount of heat dissipated to the ambient environment asa function of ambient temperature as measured by a temperate sensor ordetermined according to the resistance of the windings.

The rotor controller 43 may also determine a thermal model for thealternator. In every application, an alternator may have differentthermal properties. The thermal properties may depend on thesurroundings of the alternator. One primary consideration may be theproximity of a turbocharger to the alternator because a turbochargerheat at a high rate due to high temperature of housings. The rotorcontroller 43 may receive a temperature of the alternator from atemperature sensor mounted on the PCB assembly 40. The rotor controller43 may control field current according to this thermal model. The rotorcontroller 43 may compare the temperature to a threshold. Whentemperatures get too high or exceeds the threshold, the rotor controller43 reduces the field current. The field current may be reduced by apredetermined amount, a percentage of the field current, or by an amountproportional to the deviation in temperature. When the field current islowered, insufficient power may be supplied to the load. However, inmost applications sacrificing output is preferable to permanentlydamaging the alternator.

In many generator applications, an error may be detected, for example,in the output voltage or current that could be caused by a problem inthe normal functioning of the generator (e.g., the generator is notmaking power as expected), but could also be caused by a loss of sensing(e.g., the circuit that detects the output is failing). Using statorside controllers or voltage regulators, it is not possible todistinguish between these two scenarios.

However, with the rotor controller 43, which is mounted to the rotor androtates along with the field windings, more conclusive tests may beperformed to provide a fail safe operation. The rotor controller 43identifies the output level (voltage or current) either by loadcharacterization, as described above, or by calculating stator current,as described in association with FIG. 22 and other examples above. Therotor controller 43 may receive a measurement of the output level fromthe stator controller 50 through the rotor communication device 608receiving data from the stator communication device 618. The rotorcontroller 43 also identifies the field current. One example techniquefor measuring field current is shown in FIG. 4A and described herein.Other examples are possible.

The rotor controller 43 monitors the field current and the output level.If the output level remains relative constant (e.g., within apredetermined range), or changes within the predetermined based onchanges in the field current, there are no errors. If the ability todetect output level is lost, output voltage will remain approximatelyconstant. The output controller 43 may monitor changes in the fieldcurrent as an estimation of output level.

A significant advantage is realized when a loss of sensing occurs.Without an onboard rotor controller, when there is an apparent short onthe load, the generator controller turns the field current to a maximumlevel (e.g., full on) in an effort to maintain the output voltage. Theincrease output may clear the fault when the apparent short is really ashort on the load. When the short is real, the output voltage isdetected as dropping or nearing zero. But in other cases the problem maybe a loss of sensing. In a loss of sensing condition, a wire has becomedisconnected in the measurement circuit. The real output voltage remainsunchanged. However, the sensing has experienced an error.

The rotor controller 43, on the other hand, monitors both the outputlevel and the field current. The rotor controller 43 may identify a lossof sensing situation when the output level deviates significantly (e.g.,more than a predetermined range), or changes more than the predeterminedrange based on detected changes in the field current. In other words,when the field current behaves as expected, but the measured outputlevel changed significantly, the rotor controller 43 determines that aloss of sensing has occurred.

In response to the identified loss of sensing, the rotor controller 43may log the error, report the error, or take a corrective measure. Therotor controller 43 may log output levels and timestamps when the fieldcurrent remains unchanged or at expected levels. The rotor controller 43may report the error to the user via a display on the user interface, amessage to a mobile device, or an audible message. The message mayindicate that a sensing circuit is malfunctioning. The rotor controller43 may report the error to the stator controller 50 or generator systemcontroller 43. The rotor controller 43 may take a corrective measure bydispatching a field technician or running a diagnostic test on thesensing circuit. In one example, the sensing failure may be aggregatewith other errors from other testing in the generator in an error score.When the aggregate error score exceeds a maximum level, the rotorcontroller 42 generates a command to turn off the generator. In oneexample, the corrective measure or the report of the error may indicatethat either the sensing circuit or sensors should be replaced orrepaired.

In addition or in the alternative, the rotor controller 43 may detectharmonics in the field current. When the loss of output voltage iscaused by a short circuit, there is often a high circulating harmonic.The circulating harmonic may be a third order harmonic. The rotorcontroller 43 may detect the existence of a third order harmonic basedon frequency. The rotor 43 controller may compare the voltage/current ofthe harmonic to a threshold. The rotor controller 43 may detect thephase that the harmonic is on.

The total harmonic distortion (THD) of the output of the generator is ameasurement of the harmonic distortion present. THD may be defined asthe ratio of the sum of the powers of all harmonic components to thepower of the fundamental frequency. Alternatively, the THD may include apredetermined number of harmonics (e.g., 3, 5, 7, or 11).

The deviation between the alternator output and the sine wave may becontributed to harmonics in the alternator output. The harmonics may becaused by the geometric shape of the alternator and the finite nature ofthe stator windings. The perfect alternator may be a perfectly rounddevice with perfectly sinusoidally distributed windings around thestator interior diameter that provides a perfect sinusoid. Such analternator is not possible to construct. In practice, windings of thealternator are distributed in a finite number of slots. The rotor cannotbe perfectly round. The resulting waveform is imperfect. The shape ofthe resulting waveform may be expressed as a sum of sinusoids of varyingorder.

The periodic wave form can be expressed as a sum of odd orderedsinusoids of varying frequency. In one example, the first order sinusoidhas a frequency of 50 or 60 Hz, the third order has a frequency of 150or 180 Hz, and so on. Detectable harmonics in a three phase alternatormay include the 5^(th) order, the 7^(th) order, the 9^(th) order, the11^(th) order, and/or other harmonics. Because of the saturation orhysteresis in the core of the alternator, the attenuation of eachharmonic increase as the frequency increases. Thus, the 3^(rd) and5^(th) harmonics are the most detectable.

The rotor controller 43 may develop a profile for the generator. Theprofile describes a periodic fluctuation in an operating characteristicfor the generator. The profile may be accessed from a database oranother memory in communication with the rotor controller 43. Theoperating characteristic may be the speed of the alternator or shaft 39,or the field current of the rotor windings in the exciter armature 601or the field coil assembly 602. The profile may be adaptively learnedfrom the system over time.

The values for the profile may be measured by the pickup coil 133, whenthe profile is a speed profile, according to embodiments described abovefor determining the speed of the generator. Alternatively, anothersensor mounted on the rotor may directly detect the movement of acomponent such as a crankshaft, the gear box, transmission, armature, oranother component. The direct type of sensor may be a torque sensor, adeflection sensor, a dynamometer, a positional sensor, or a revolutionsensor.

The deflection sensor may measure a deflection of the crankshaft oranother device. The deflection sensor may include two position sensors.The position sensors may be associated with different ends of the rotorshaft. As an example, the sensor may be a positional sensor (e.g.,position sensor or accelerometer) that may measure the change inrotation of a crankshaft or other component of generator. The revolutionsensor may be a magnetic sensor that detects a change in a magneticfield, an optical sensor that detects indicia on the component, acontact sensor that detects a tab or protrusion on the crankshaft, oranother component.

The values for the profile may be measured by the a detection circuitcoupled to the exciter armature 601 or the field coil assembly 602, whenthe profile is a field current profile, according to embodimentsdescribed above for calculating the field current.

The rotor controller 43 is configured to generate, control, or modify afield current for the alternator based on the profile, which may be thespeed profile, the field current profile, or both, that describes theperiodic fluctuation in the operating characteristic for the generator.

The field current profile may be adjusted to reduce the distortioncaused by the harmonics, which may be referred to as total harmonicdistortion (THD), to a threshold level. Example THD thresholds include1%, 2%, 5% and 10%. Without field current control, design of a generatorto meet the 1%, 2%, or even 5% THD threshold may come at a cost toefficiency or significant material expense. However, controlling or finetuning the field current profile can eliminate or reduce the effects ofthe harmonics in the output and meet very low THD thresholds, whilemaintaining near-optimal efficiency and material costs.

FIG. 25A illustrates an example speed profile for a generator. The speedprofile may be continuous or discrete. The speed profile may fluctuatebetween a maximum frequency and a minimum frequency. The frequency maybe measured in rotations per unit time. The speed profile may be afunction of the combustion cycle of the engine and/or the physicalconstruction of the generator. The speed profile may be periodic. Theperiod of the speed profile (Tp) may depend on the diameter of the rotoror the average speed of the alternator. The circumference of the rotordivided by the average frequency (rotations per unit time) provides theamount of time for one rotation, which may be the period of the speedprofile (Tp). The period of the speed profile (Tp) may span the lengthof time for the all of the cylinders to fire. The illustrated example inFIG. 25A may be a 3 cylinder engine, thus three peaks are included inthe speed profile (Tp). The interval Ts corresponds to the time periodthat corresponds to one of the cylinders.

The output is considered congruent to the speed profile based on therelative change in ratios between the speed profile and the output. Inone example, the two shapes are considered congruent based on the ratiosto the minimum values and maximum values of the shapes. For any period,the ratio of the maximum value of the speed profile value to the maximumvalue of the output is calculated and the ratio of the minimum value ofthe speed profile value to the minimum value of the output iscalculated. When the difference between the ratios is within apredetermined range, the two shapes are considered congruent. Examplesfor the predetermined range include 0.8 to 1.05 and 0.9 to 1.1. Inaddition or in the alternative, the two shapes may be consideredcongruent when one or more maximum values of the speed profile occurwithin a predetermined time period of one or more maximum values of theoutput and/or one or more minimum values of the speed profile occurwithin a predetermined time period of one or more minimum values of theoutput. Example predetermined time periods include 5 milliseconds and 10milliseconds.

FIG. 25B illustrates an example modified field current according to thespeed profile of FIG. 25A. The speed profile of FIG. 25A is illustratedto show the changes in the modified field current track changes in thespeed profile. The modified field current may be inversely proportionalto the speed profile. The inversely proportional relationship may beconstant throughout period Tp or may fluctuate with a predeterminedrange. The predetermined range may be plus or minus any percentage valuefrom 1% to 15%.

In another example, the modified field current may be inverselycongruent to the speed profile. In one example, the two shapes areconsidered inversely congruent based on the ratios to the minimum valuesand maximum values of the shapes. For any period, the ratio of themaximum value of the speed profile value to the corresponding minimumvalue of the output is calculated and the ratio of the minimum value ofthe speed profile value to the corresponding maximum value of the outputis calculated. When the difference between the ratios is within apredetermined range, the two shapes are considered inversely congruent.Examples for the predetermined range include 0.8 to 1.05 and 0.9 to 1.1.In addition or in the alternative, the two shapes may be consideredinversely congruent when one or more maximum values of the speed profileoccur within a predetermined time period of one or more minimum valuesof the output and/or one or more minimum values of the speed profileoccur within a predetermined time period of one or more maximum valuesof the output. Example predetermined time periods include 5 millisecondsand 10 milliseconds. Alternatively, FIG. 25A illustrates an exampledetected field current at the field coil assembly 602. Because ofvariances in materials and machine properties. The detected fieldcurrent may differ from the rotation of the exciter armature 601. Inthis case FIG. 24B illustrates a modification to the field current inorder to account for the irregular shape. Specifically, FIG. 25Aillustrates an example speed profile from a 3-cylinder engine,illustrating variations in the output speed for every firing event (3events per 2 revolutions). The target field current is determined insuch a way that the product of field current and synchronous speedremains constant or providing a nearly constant voltage.

The field current control may be activated and deactivated according toa control signal. The control signal may be generated based oninstructions received from a user, a predefined schedule, or a feedbackcontrol system. The field current control activation signal may betransferred to the rotor controller using digital communication. Theuser may activate or deactivate the field current control through aswitch, button, or other setting on the generator, which triggers thecontrol signal. The user may remotely send a command to the generatorcontroller through a mobile application or a website. The predefinedschedule may activate the field current control during peak hours anddeactivate the field current control outside of peak hours. The feedbackcontrol system may monitor the output of the generator (e.g., voltagesensor or current sensor) and activate the field current control whenthe output exceeds a threshold value. The threshold value may be apercentage of the average output (e.g., 5% or 10%), a number of standarddeviations from the mean output (e.g., 1 standard deviation), or a setvalue (e.g., 100 volts, 130 volts).

The values that make up the speed profile may fluctuate according tocombustion cycles of the engine. Thus, the shape or variance of thespeed profile may be a function of the number of cylinders of theengine. An engine with four or more cylinders may have a speed profilewith low variance because one cylinder out of the four or more cylindersis usually firing or approaching firing. That is, the crankshaft hasless time to decelerate after a power stroke of one cylinder before apower stroke of another cylinder begins. The combustion cycles of anyone cylinder is balanced by the combustion cycles of the othercylinders.

On a single cylinder engine, the speed profile has a high variancebecause there are no other cylinders to balance the combustion cycles ofthe single cylinder. The compression stroke significantly slows down theengine (e.g., extracts power from the crank shaft) and the power strokesignificantly speeds up the engine (e.g., adds power to the crankshaft). The intake stroke and top stroke may slow down the engine to alesser extent.

In a two cylinder engine, the speed profile may have a medium variancefor reasons similar to the four cylinder engine discussed above.However, for a two cylinder odd fire engine, the speed profile may havea high variance (e.g., even higher than in the one cylinder example). Ina two cylinder odd fire engine, the cylinders fire close together intime. In one example, during the 360 degrees rotation of the crankshaft,the first cylinder fires at 270 degrees and the second cylinder fires at450 degrees (90 degrees of the subsequent cycle). The speed of thecrankshaft may reach a first maximum after the first cylinder fires anda second, higher maximum after the second cylinder fires.

The speed profile of an engine with an odd number of cylinders may havea variance because the cycles of the engine and the alternator may beout of synch. A three cylinder engine may fire every 240 degrees. Thealternator may be a two pole alternator that takes power every 180degrees or a four pole alternator that takes power every 90 degrees. Ineither case, there may be aliasing between the alternator and the enginebecause the engine fires and the alternator draws power at varying timesrelative to each other.

FIG. 26 illustrates an example output for a generator with field currentcontrol deactivated. Because the field current control is deactivated,the field current, as shown by dash line 411 is substantially constant.Window 401 illustrates the deviation between the alternator output, asshown by solid line 413, and an ideal sine wave, as shown by the dottedline 415. The rotor controller 43 is configured to adjust the fieldcurrent to vary over time, which brings the solid line of the ideal sinewave 415 and the alternator output 413 together. The alternator output413 may be equal to a sinusoid or within a tolerance range (e.g., 1% or5%) of a perfect sinusoid. The deviation from a perfect sinusoid is morecommonly referred to as THD, as described above. The rotor controller 43may provide a variable speed support for doubly-fed inductionfunctionality on an alternator. A doubly-fed induction machine providesa time-varying current to the rotor to allow the generator to output afrequency that differs from the operating frequency of the rotor. Thetime-varying current frequency matches the difference between the outputfrequency and the rotor synchronous frequency. Some doubly-fed inductionmachines apply time-varying to the rotor using slip rings and brushes.In some doubly-fed induction machines, an AC sinusoidal bias may begenerated by the voltage regulator or stator controller 50. The AC biasmay be applied to the rotor field current using slip rings or brushes.

The alternator runs at a synchronous speed, depending on a number ofpoles, to output the rated frequency (e.g., 60 Hz). In some instancesthe synchronous speed for the mechanical rotation may not produce thedesired power. For example, consider a speed is 1800 rpm for a 4 polegenerator, and one example in which the generator is producing 9 kW but10 kW is desired. The engine can be run at 2000 rpm rather than 1800 rpmto get to 10 kW. However, the output would be at 66.6 Hz. A reverse ACbias of 6.6 Hz is impressed on the field current to cause a reversefield and correct the output frequency to approximately 60 Hz.Similarly, the engine or prime mover can be run slower than synchronousspeed and a forward bias is impressed on the field current to speed upthe output. This technique can allow the engine to be run slower, whichreduces noise and fuel consumption.

The rotor controller 43 may provide similar control without slip ringsor brushes because the rotor controller 43 is supported by and rotatingalong with the rotor assembly. The rotor controller 43 may identify anoverspeed situation by monitoring the speed of the rotor based on theoutput of the pickup coil 133 or any of the sensor techniques describedherein. When the speed exceeds the rated speed of the generator oranother threshold value, the rotor controller 43 may identify that thegenerator is in an overspeed condition.

The rotor controller 43 may calculate an AC bias based on the overspeedcondition. For example, a frequency of the AC bias may be theproportional amount by which the rated speed is exceeded. As describedby Equation 7, the frequency (F) of the AC bias is equal to the productof the rated frequency (F_(R)) of the generator times the ratio of themeasured speed (S) to the rated speed (S_(R)).

$\begin{matrix}{F = {F_{R}{\frac{S}{S_{R}}.}}} & {{Eq}.\mspace{14mu} 7}\end{matrix}$

Communication between the stator and rotor is provided by the rotorcommunication device 608 and the stator communication device 618. Thecommunication may take various forms including but not limited tooptical communication, radio communication, and magnetic communication.

FIG. 27 illustrates an example rotor 90 including the rotorcommunication device 608 using an arrangement of magnetic coils 91. FIG.28 illustrates an example stator communication device 618, alsoincluding an arrangement of magnetic coils 97. Current flowing throughthe magnetic coils in the rotor communication device is controlled totransfer data to the stator communication device 618 by inducing amagnetic flux in coils in the stator communication device 618.Communication may similarly be performed in the direction from thestator communication device 618 to the rotor communication device 608.

The magnetic coils 91 and 97 may be arranged in concentric circles forsignal immunity. Each coil in the circle may apply the same signal anddata. Thus, no matter the position of the rotor the coils are aligned.In addition, redundancy may protect the communication signals frominterference from cellular phones, microwaves, or other devices.

Alternatively, different data may be transmitted in the coils arrangedin a circle. Because each coil is always aligned with another coil, thedata can be successfully transmitted between the rotor and the stator.The magnetic coils 91 and 97 may be half-duplex or full-duplex. In halfduplex, one set of coils transmits data from the rotor to the stator,and another set of coils transmits data from the stator to the rotor. Infull duplex, one set of coils may transfer data in both directions. Fullduplex operation may be achieved using one frequency for a sendingchannel and another frequency for a receiving channel. In some cases,communication can by frequency-coded, in other cases, communication canbe amplitude-coded or phase-coded.

Examples of content communicated from the stator communication device618 to the rotor side communication device 608 may include theelectrical properties or output characteristics of the generatorcollected by or calculated by the stator controller 50. In addition, thestator communication device 618 may send data to the rotor controller 43such as potential firmware updates, power over serial, fault codes,historical events, and waveform capture. The rotor may communicate datato the stator. This data may consist of: field current, field voltage,rotor temperature, magnetic field intensity, stator current, alternatorreal power, alternator apparent power, alternator reactive power,alternator type, parameters settings, waveform snapshots, faultconditions, stored data, instantaneous data, measured data, orcalculated data.

In addition or in the alternative, the stator communication device 618may provide power to the rotor controller 43 and/or PCB assembly 40using the communication interfaces. For example, the statorcommunication device 618 and the rotor communication device 608 may actas a transformer for sending power from the stator to the rotor to powerelectrical components on the rotor.

In one example, the stator communication device 618 and the rotorcommunication device 608 are used in limited circumstances. The rotorcontroller 43 may store a data log in a black box device. The black boxdevice is a memory configured to record data collected or calculated bythe rotor controller. The black box device may be formed of or encasedin a heat and/or fire resistant material. The rotor controller 43 maystore output levels (e.g., voltage, current, or power), field currentlevel, user settings, error messaged, or any of the data readingsdescribed herein.

In one embodiment, the black box device is read when the generator istaken in for servicing, the black box is read to retrieve the previouslyrecorded data. The service technician may troubleshoot the generatorbased on the recorded data. The black box device may include a universalserial bus (USB) or another connection to retrieve the recorded data. Inanother embodiment, after the generator experiences a catastrophicfailure, the black box device is read to determine what caused thecatastrophic failure.

The rotor controller 43 may also perform damper bar control. FIG. 29illustrates an example rotor 140 including damper bars 141 and a switcharray 143. A predetermined number of damper bars per pole may beincluded. The damper bars 141 may be grouped in inside damper bars 141 band outside damper bars 141 a. While two are shown, there may be one orany number of damper bars in the in inside damper bars 141 b and outsidedamper bars 141 a.

The damper bars 141 may aid in the stabilization of the power angle whenthe generator is undergoing load transient, supplying large motors, oroperating in parallel. The stabilization occurs due to a torquegenerated by a slip in speed of the rotor and the rotating magnetic fluxin the stator (similar behavior to an induction machine. The damper bars141 may reduce the counter rotating armature reaction component, ormegnetomotive force (MMF), in the field windings when the alternator isproviding stator current. The damper bars 141 may reduce THD, when thealternator is providing stator current, by equalizing the magnetic fluxdistribution in the rotor especially in single-phase conditions.

Fewer damper bars may be needed for certain loads, and fewer damper barsmay be needed when all three phases are loaded. Unnecessary damper barscause extra heat to be dissipated and also wasted energy to be consumed.Thus, the rotor controller 43 may selectively control the damper bars141.

In one example, the rotor controller 43 may detect whether apredetermined load is on each phases of the generator. When thepredetermined load is exceeded, a set of damper bars (e.g., in insidedamper bars 141 b or outside damper bars 141 a) is deactivated bysending a switch command to the switch array 143. In one example, therotor controller 43 may monitor THD. When THD is lower that a thresholdTHD level, only one set of damper bars is activated, and when the THD ishigher that the threshold THD level, both sets of damper bars areactivated by the rotor controller 43 sending the switch command to theswitch array 143.

Besides, the inside damper bars 141 b and outside damper bars 141 a, thedamper bars may be classified as shallow bars and deep bars. The shallowbars are closer to the outer circumference of the rotor than the deepbars. The rotor control 43 may activate the shallow bars for a startupphase or a high torque condition of the alternator and activate the deepbars for the running phase or a low torque condition of the alternator.The rotor control 43 may activate the deep bars for a startup phase or ahigh torque condition of the alternator and activate the shallow barsfor the running phase or a low torque condition of the alternator.

The rotor controller 43 may detect parameters of the rotor and classifythe rotor, alternator, or generator based on the detected parameters. Amemory for the rotor controller 43 may store a lookup table thatassociates rotor parameters with a model number for the alternator orthe generator, a manufacturer for the alternator or the generator, or amachine type for the manufacturer or the alternator. The rotorparameters may include rotor resistance, rotor inductance, a number ofwindings, a property of the field current, number of poles, rotorwinding capacitance to ground, rotor field winding capacitance, numberof damper bars, ratio of inductance to resistance, natural resonancefrequency, damper winding inductance, damper winding resistance, otherfactors can also be used. Alternatively, exciter parameters may be usedsuch as exciter Information, exciter pole count, exciter Inductance,exciter resistance, exciter voltage at a given speed, or exciterperformance measurements (e.g., acceleration rate, cranking speed, ordeceleration rate). In another example, machine information may be usedsuch as a machine constant (e.g., a ratio of field current to outputvoltage), stator inductance, or stator resistance.

The rotor parameter may include a single measured value or a combinationof measured values. For example, a combination of a rotor resistance ina range of resistances and a number of windings in another range mayindicate that the alternator is a particular model or from a particularmanufacturer. In this way, the rotor controller 43 may be operable withmany types of alternators or generators without user intervention. Anyof the examples described herein may be based on the detected alternatoror generator.

The rotor controller 43 may be operable in multiple modes. In a firstmode, the rotor controller 43 detects the rotor parameters and consultsthe lookup table at first start up. That is, the rotor controller 43performs the classification of the rotor, alternator, or generator onlyonce, when the rotor controller 43 initializes. In a second mode, therotor controller 43 detects the rotor parameters and consults the lookuptable at every power cycle. In either mode, the detection may berestarted based on a user input or master reset. The rotor controller 43may log each detection and master reset in combination with a timestampin memory.

FIG. 30 illustrates an example rotor controller 43. The rotor controller43 may include a processor 300, a memory 352, and a communicationinterface 353. The rotor controller 43 may be connected to a workstation359 or another external device (e.g., control panel) and/or a database357 for receiving user inputs, system characteristics, and any of thevalues described herein. Optionally, the rotor controller 43 may includean input device 355 and/or a sensing circuit 311. The sensing circuit311 receives sensor measurements from as described above. Additional,different, or fewer components may be included. The processor 300 isconfigured to perform instructions stored in memory 352 for executingthe algorithms described herein. The processor 300 may identify anengine type, make, or model, and may look up system characteristics,settings, or profiles based on the identified engine type, make, ormodel.

The processor 300 may include a general processor, digital signalprocessor, an application specific integrated circuit (ASIC), fieldprogrammable gate array (FPGA), analog circuit, digital circuit,combinations thereof, or other now known or later developed processor.The processor 300 may be a single device or combinations of devices,such as associated with a network, distributed processing, or cloudcomputing.

The memory 352 may be a volatile memory or a non-volatile memory. Thememory 352 may include one or more of a read only memory (ROM), randomaccess memory (RAM), a flash memory, an electronic erasable program readonly memory (EEPROM), or other type of memory. The memory 352 may beremovable from the network device, such as a secure digital (SD) memorycard.

In addition to ingress ports and egress ports, the communicationinterface 303 may include any operable connection. An operableconnection may be one in which signals, physical communications, and/orlogical communications may be sent and/or received. An operableconnection may include a physical interface, an electrical interface,and/or a data interface.

The communication interface 353 may be connected to a network. Thenetwork may include wired networks (e.g., Ethernet), wireless networks,or combinations thereof. The wireless network may be a cellulartelephone network, an 802.11, 802.16, 802.20, or WiMax network. Further,the network may be a public network, such as the Internet, a privatenetwork, such as an intranet, or combinations thereof, and may utilize avariety of networking protocols now available or later developedincluding, but not limited to TCP/IP based networking protocols.

While the computer-readable medium (e.g., memory 352 or database 357) isshown to be a single medium, the term “computer-readable medium”includes a single medium or multiple media, such as a centralized ordistributed database, and/or associated caches and servers that storeone or more sets of instructions. The term “computer-readable medium”shall also include any medium that is capable of storing, encoding orcarrying a set of instructions for execution by a processor or thatcause a computer system to perform any one or more of the methods oroperations disclosed herein.

In a particular non-limiting, exemplary embodiment, thecomputer-readable medium can include a solid-state memory such as amemory card or other package that houses one or more non-volatileread-only memories. Further, the computer-readable medium can be arandom access memory or other volatile re-writable memory. Additionally,the computer-readable medium can include a magneto-optical or opticalmedium, such as a disk or tapes or other storage device to capturecarrier wave signals such as a signal communicated over a transmissionmedium. A digital file attachment to an e-mail or other self-containedinformation archive or set of archives may be considered a distributionmedium that is a tangible storage medium. Accordingly, the disclosure isconsidered to include any one or more of a computer-readable medium or adistribution medium and other equivalents and successor media, in whichdata or instructions may be stored. The computer-readable medium may benon-transitory, which includes all tangible computer-readable media.

In an alternative embodiment, dedicated hardware implementations, suchas application specific integrated circuits, programmable logic arraysand other hardware devices, can be constructed to implement one or moreof the methods described herein. Applications that may include theapparatus and systems of various embodiments can broadly include avariety of electronic and computer systems. One or more embodimentsdescribed herein may implement functions using two or more specificinterconnected hardware modules or devices with related control and datasignals that can be communicated between and through the modules, or asportions of an application-specific integrated circuit. Accordingly, thepresent system encompasses software, firmware, and hardwareimplementations.

We claim:
 1. A method comprising: receiving, at a generator controller,inductance data for a change in inductance for an alternator wherein thegenerator controller rotates with a rotor of the alternator; analyzing,at the generator controller, a change in the inductance data; andgenerating, at the generator controller, a generator command based onthe inductance data.
 2. The method of claim 1, wherein generating thegenerator command comprises: adjusting a target field setting based onthe change in the inductance data; and changing a driving characteristicof a field winding based on the target field setting.
 3. The method ofclaim 1, wherein generating the generator command comprises: adjusting acurrent in a field winding of the alternator.
 4. The method of claim 1,wherein generating the generator command comprises: adjusting a speed ofan engine driving the rotor.
 5. The method of claim 1, whereingenerating the generator command comprises: shutting down thealternator.
 6. The method of claim 1, wherein the inductance datadescribes an inductance induced on a coil of the rotor of the alternatorby a stator of the alternator and the inductance data is indicative ofthe output of the alternator through a magnetic coupling between therotor and the stator.
 7. The method of claim 1, wherein the coil is apickup coil mounted on the rotor or the coil is a field winding.
 8. Themethod of claim 1, wherein the analysis includes a query for a lookuptable using the inductance data.
 9. The method of claim 1, wherein theinductance data is indicative of a load electrically connected to thealternator.
 10. The method of claim 1, further comprising: sending,using a communication interface, the generator command to an externalcontroller.
 11. The method of claim 10, wherein sending the generatorcommand comprises: generating at least one magnetic signal for aconcentric arrangement of magnetic coils.
 12. An apparatus comprising: asensor configured to detect a change in inductance for an alternator;and a generator controller configured to analyze a change in theinductance data and generate a generator command based on the inductancedata, wherein the generator controller rotates with a rotor of thealternator.
 13. The apparatus of claim 12, wherein the generator commandincludes adjustment of a target field setting based on the change in theinductance data and adjustment of a driving characteristic of a fieldwinding based on the target field setting.
 14. The apparatus of claim12, wherein the generator command includes adjustment of a current in afield winding of the rotor of the alternator.
 15. The apparatus of claim12, wherein the generator command includes adjustment of a speed of anengine driving the rotor.
 16. The apparatus of claim 12, wherein thegenerator command includes a command to shut down the alternator. 17.The apparatus of claim 12, wherein the inductance data describes aninductance induced on a coil of the rotor of the alternator by a statorof the alternator and the inductance data is indicative of the output ofthe alternator through a magnetic coupling between the rotor and thestator.
 18. The apparatus of claim 12, wherein the inductance data isindicative of a load electrically connected to the alternator.
 19. Theapparatus of claim 12, further comprising: a communication interfaceconfigured to send the generator command with at least one magneticsignal.
 20. A method comprising: generating, at a sensor, inductancedata for a change in inductance for an alternator wherein the generatorcontroller rotates with a rotor of the alternator; analyzing, at thegenerator controller, the inductance data; and generating, at thegenerator controller, a generator command in response to the inductancedata, wherein the generator command is configured to adjust a current ina field winding of the alternator.